What you want is Anti Aliasing. Blockland doesn't have a default setting for it, but in msot graphic cards you can set it to override blockland's default '0' value.What kind of graphics card do you have?
I couldn't find any info online but you need open the graphics card control panel, (Maybe through Windows control panel?) find some sort of 3D or game settings (not video/movie), and change the anti-aliasing value to 2x or more. Make sure you have the latests drivers too. What OS do you have? This seems to be the latest driver for Windows XP: http://www.nvidia.com/object/winxp-306.81-whql-driver.html